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 Post subject: Wiring up the charging system
PostPosted: Wed Jan 01, 2014 2:37 am 
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Joined: Wed Mar 25, 2009 12:06 pm
Posts: 135
Location: Brisbane, Australia
model: 906 Paso
year: 1990
I just redid my wiring harness and struggled to get the charging wiring connections right, but it's sorted now. I read some threads here and in the 750 forum:

This is my summary:

The Paso alternators are apparently single phase with the OEM having three wires (two yellow output, one red). It seems the red wire was needed with the OEM RR, but if you upgrade to an aftermarket RR where the internal wiring is different it seems it is unlikely you will need the red wire.

I have an RR51 from When I looked at their diagram at I thought I was supposed to wire up the red and split one yellow from the RR to connect to the red. When I did that the battery was not charging. The volts were dropping on the battery reading below 12V when idling and riding (which I understand is a problem).

Then I read that pdf properly. You can see in the instructions, "For models fitted with 3 cables from the alternator/generator (2 yellow and red) [which is the OEM stator, I believe], check the voltage between the 2 yellow cables. If the reading is between 50 - 100 use diagram 1 and ignore the red cable. If the reading is 0 use diagram 2." So, I checked the AC voltage and sure enough it was between 50-100, so I went back to wiring as per diagram 1 and it works now so the battery shows ~14V when idling. All good.

So then you just ignore the red wire at the OEM stator if you have upgraded the RR such as the RR51 from

I hope that helps.

P.S. I also did some testing on the RR51 and the stator:
- I looked on YouTube on checking an RR using the Diode setting on a voltmeter. Following that I found my RR51 was getting the right readings for the two yellow wires that matter - not to worry about the red and blue. Seemed okay.
- Then I did some voltmeter testing on the stator. 0.1-2.0 Ohms between the two yellows (good), no reading when earthing either of the yellows (good). Then with the bike running checking the AC volts were good (50-100V AC) between the two yellows (good). Seemed okay.

Warwick - on a learning curve and on a
Ducati Paso - Soul of a thoroughbred :P

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 Post subject: Re: Wiring up the charging system
PostPosted: Fri Jan 03, 2014 8:59 pm 
paso grand pooh-bah
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Joined: Sat Sep 03, 2005 12:00 am
Posts: 1318
Location: SF Bay Area
model: 750 Sport
year: 1990
Thanks for your writeup. Yes, the stator is a single phase, and the red wire is a spur off the middle of the winding for some unknown reason, and ends up going no where. I too hooked it up to a regulator, only to find it didn't charge at all.

With all of the charging systems, the connectors are the weak link. I have taken to simply cutting the connectors off, and soldering the wires in place. If I need to change something, I'll just re-solder them. My project bike has the alternator wires melted at the connectors, so I'll be trimming the wires back to where they are reasonable, and soldering them up. I'm almost tempted to run a new pair of wires all the way to the stator, but that's a bit more work that I will save for when the current wires fail completely.

I used the RR51 on my 98 ST2, and it worked fine. It should hold up fine in the Paso, as it has much less amperage.

Cheers, phil

Duc in the Bay
1990 750 Sport x2-Rosso Blanko (900ss copy) & Nuovo Nudo (Scrambler project)
1991 907 -mostly stock
2002 ST4s - Lots of mods.

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